It’s very common task in Java to format double to 2 decimal places – usually to format currency. It’s not easy to do correctly, but in this post we’ll show how.
Round double using String.format
The simplest way to print double rounded to two decimal places is to use String.format as here:
double number = 12.5678;
String s = String.format("%.2f", number);
System.out.println(s);
It prints the rounded value:
12,57
Note the comma in the formatted string. It is because String.format is using the current Locale and in my case it is pl_PL. In English locale it would print dot instead of comma.
String.format prints leading zero
This way of formatting double preserves leading zero, unlike some other number formatting:
double number = 0.5678;
String s = String.format("%.2f", number);
System.out.println(s);
The above code produces the following output:
0,57
Round double using DecimalFormat
As String.format() above java.text.DecimalFormat is using default Locale to format numbers, so it will print formatted number with dot or comma as separator between integer and decimal parts:
DecimalFormat df = new DecimalFormat("#.##");
String s = df.format(1234.5678);
System.out.println(s);
## means that there should be at most 2 decimal numbers:
1234,57
DecimalFormat ## remove trailing zeros
Note that # in the format means that the digit at that position is optional and won’t be printed if it not needed. This happens with trailing zero here:
DecimalFormat df = new DecimalFormat("#.##");
String s = df.format(123.0);
System.out.println(s);
It prints:
123
DecimalFormat “00” to preserve trailing zeros
To force DecimalFormat to preserve specified number of trailing zeros use “00“:
DecimalFormat df = new DecimalFormat("#.00");
String s = df.format(123.0);
System.out.println(s);
Now double is formatted with trailing zeros:
123,00
Round double using NumberFormat – custom Locale
java.text.NumberFormat is the most flexible class, but also the most cumbersome to use. It allows to set Locale and specify number formatting parameters:
Locale locale = Locale.ENGLISH; NumberFormat nf = NumberFormat.getNumberInstance(locale); // for trailing zeros: nf.setMinimumFractionDigits(2); // round to 2 digits: nf.setMaximumFractionDigits(2); System.out.println(nf.format(.99)); System.out.println(nf.format(123.567)); System.out.println(nf.format(123.0));
In the above code we set English Locale, and set double format to always have 2 decimal digits. The output is as expected:
0.99 123.57 123.00
Note the dot as separator in formatted number!
